Many have considered it desirable to build engines running at higher temperatures. Efficiency would improve, since it is dependent on the difference in temperature between ambient air (which is constant) and that at combustion. The resulting hotter exhaust gases will generally be easier to cleanse. If the cooling system can be eliminated, so can its cost, mass, bulk and unreliability. Un-cooled engines can be thermally, acoustically and vibrationally insulated to virtually any degree, making them more environmentally and socially acceptable. Of the calorific value of the fuel, a greater amount will be spent on pushing a piston, but nearly all the remainder will now be in the hot exhaust gas, where it is recoverable. With the new engines, temperature equilibria would be so high that the main piston and cylinder components would likely have to be of ceramic material.
To the knowledge of the applicant, un-cooled engines are not in production today. Manufacturers and researchers tried to build what they called “adiabatic” semi-un-cooled engines in the late 1980's and early 1990's. Publications indicate the work nearly all involved substituting ceramic materials for metals in key combustion chamber components. For example, ceramic caps were placed on metal pistons; ceramic liners placed in metal engine blocks; a zirconia poppet valve was substituted for an identically shaped metal valve. The work was not very successful for a number of reasons, including problems with differential thermal expansion of ceramic and metal components abutting each other. Engine designs were essentially unchanged.
Early internal combustion (IC) engine designers like Gottfried Daimler and Rudolf Diesel adapted the mid-18th century metal piston-and-cylinder technology developed for steam engines. Today's metal IC engines reflect three constraints; the materials characteristics of metals; the need for cooling and therefore the engine block, etc; and commercial practice determining the most viable ways of manufacturing and assembling metal components.
The applicant felt that any viable commercial embodiment of the un-cooled ceramic engine would look very different from today's units, because all the old constraints were no longer relevant, and new constraints would apply. This disclosure is the result of his attempt to adapt and modify the traditional design of the piston and cylinder engine, so that new embodiments could be viably built un-cooled and out of ceramic material. Because exhaust emissions control is so important today, new arrangements for cleansing high temperature exhaust gases were devised, and are disclosed herein.
In today's typical engine, roughly one third of the calorific value of the burnt fuel is put to work driving the piston, one third is dissipated via the cooling system and general radiation by the engine components and one third is carried away by the exhaust gases. The latest large diesels for trucks and marine applications have efficiencies in the 40% range, but the average for all engines now operating is close to 30%. These figures are for efficiencies on the piston crown, for new engines, in the optimum operating mode. Real-world efficiencies at the output shaft for all engines in the field, under all operating conditions, are far, far lower. Current large engines, as used in ships and electricity generating stations, often have some form of compounding, which entails using a device (say a turbine) to derive further work from the hot exhaust gases.
In un-cooled engines, the combustion process takes place at higher temperatures, leading to efficiency increases of anywhere between 0 and 20%, dependant on design and construction details.
A conservative projection could be 10%, enough to make to make a substantial difference to the oil needs and political situation of a country such as the USA. In compounded un-cooled engines greater efficiencies can be expected, since the exhaust energy conversion devices have a greater portion of the fuel's calorific value to work with—somewhere between 50 and 60% could be in the hot exhaust gas. Turbines or steam engines may be used to extract work from the hot gas; optionally the gas heat can be converted into electrical energy.
Clarifications
By “un-cooled” is meant engines or pumps having no mechanism for transfer of heat from combustion or working volume to ambient air. Such mechanism typically comprises a water jacket, pump, radiator and fan, or comprises a fan directing air over metal cooling fins or surfaces. Un-cooled engines may have some form of charge cooling, wherein the temperature of the charge is reduced before it enters the combustion or working chamber.
The features described herein illustrate by way of example the many ways un-cooled engines and exhaust gas reaction volumes may be constructed. Any type of piston or valve may be used in an un-cooled engine and the engine portions may be assembled in any manner.
The features of the un-cooled engine have been described mainly in relation to internal combustion engines, although they are suited to and may be applied to any type of combustion engine, including for example Stirling and steam engines. The features relating to heat exchangers may be embodied in any type of engine, including conventionally cooled engines.
Where appropriate, features described herein may be applied to pumps. The word “engine” is used in its widest possible meaning and, where appropriate, is meant to include pump and/or compressor.
It is emphasized that the various features and embodiments of the invention may be used in any appropriate combination or arrangement. Where diagrams or embodiments are described, these are always by way of example and/or illustration of the principles of the invention. Further, it is considered that any of the separate features of this complete disclosure comprise independent inventions.
In the following text and recital of claims, “filamentary material” shall be defined as portions of interconnected material which allow the passage of gases therethrough and induce turbulence and mixing by changing the directions of travel of portions of gas relative to one another, the inter-connection being integral, continuous, intermeshing, inter-fitting or abutting, this definition applying to the material within the reactor as a whole as well as to particular portions of it.
By “ceramic” is meant baked, fired or pressed non-metallic material that is generally mineral, ie ceramic in the widest sense, encompassing materials such as glass, glass ceramic, shrunken or recrystallized glass or ceramic, etc., and refers to the base or matrix material, irrespective of whether other materials are present as additives or reinforcement.
By “elastomeric”, “compressible”, “elastic”, “variable volume”, “flexible”, “bending” and all other expressions indicating dimensional change is meant a measurable change that is designed for, not a relatively small dimensional change caused by temperature variation or the imposition of loads on solid or structural bodies.
By “ring valve” is meant a movable ring-shaped element normally approximately flush with a surrounding and a core surface. When the valve is actuated, it projects from any plane of the surrounding and core surface, causing fluid to flow past both the outer and the inner circumferences of the ring.
In the following text, abbreviations are used, including: rpm and rps for “revolutions per minute” and “revolutions per second” respectively, BDC/TDC for “bottom dead center/top dead center”, IC for “internal combustion”.